CN106972183B - Nanometer PPy-Au modified metal double polar plates of polymer electrolyte film fuel cell and preparation method thereof - Google Patents

Abstract

The invention provides a method for preparing a metal bipolar plate of a polymer electrolyte membrane fuel cell modified by nanometer PPy-Au. The electrochemical synthesis method is used to place the metal substrate in the electrolyte solution at a temperature of 25°C and a current of 4mA/cm ^2. Synthesize the modified layer under the conditions of ultrasonic frequency 24kHz and time 10-30min. The bipolar plate prepared by the method provided by the invention has a 2-5 μm nanometer PPy-Au modified layer on the surface of the metal substrate, the corrosion rate is lower than 6 μA/cm ² , and the contact resistance is lower than 10 mΩ·cm ² . On the premise of not affecting the strength, the method provided by the invention can realize the synchronous optimization of the corrosion resistance and surface conductivity of the metal bipolar plate, thereby achieving the purpose of improving the performance of the polymer electrolyte membrane fuel cell. The preparation method has the advantages of simple equipment and process, low cost and the like, and can realize mass production of bipolar plates.

Description

Nano PPy-Au modified polymer electrolyte membrane fuel cell metal bipolar plate and its Preparation

technical field

The invention belongs to the technical field of fuel cells. In particular, it relates to metal bipolar plates of polymer electrolyte membrane fuel cells and their surface modification.

Background technique

Polymer electrolyte membrane fuel cells have the characteristics of high energy conversion efficiency, long life, low operating temperature, environmental friendliness, and low-temperature rapid start-up. power source. However, many factors such as relatively high cost, weight, and volume largely limit the large-scale commercial production and application of polymer electrolyte membrane fuel cells. Therefore, reducing the cost of materials and preparation of its various components has always been a hot issue that governments and researchers pay attention to and urgently need to solve.

As one of the multifunctional components of the polymer electrolyte membrane fuel cell, the functions of the bipolar plate mainly include separating the reactant gas, collecting and conducting electricity, supporting the membrane electrode, providing channels for the reactant gas and making it evenly distributed, and facilitating the hydrothermal of the battery pack. manage. Graphite has good electrical conductivity and chemical stability, and is an ideal bipolar plate material for polymer electrolyte membrane fuel cells. However, the shortcomings of high brittleness, low strength, and porous structure make it difficult to produce low-weight, low-volume high-performance fuel cell stacks. In addition, the process required to process the flow field on the surface of the graphite plate is complex and expensive, accounting for about 80% of the total cost of the polymer electrolyte membrane fuel cell. Compared with traditional graphite, metal materials have obvious advantages in terms of strength, toughness, electrical conductivity, and air tightness. It is worth noting that machining and stamping methods can be used to process various shapes of flow fields on the metal surface, which is especially suitable for mass production and can greatly improve the mass specific power and volume specific power of polymer electrolyte membrane fuel cells. Currently commonly used metal bipolar plate materials mainly include iron-based alloys, nickel-based alloys, aluminum, titanium and their alloys.

Affected by the partial degradation of the proton exchange membrane and the particularity of the electrode preparation process, SO ₄ ^2- , SO ₃ ^2- , CO ₃ ^2- , HSO ₄ ^- and HSO ₃ ^- plasmas often exist in the working environment of polymer electrolyte membrane fuel cells . Therefore, electrochemical corrosion of metal bipolar plates under such acidic conditions is inevitable. Although the passivation film formed on the surface of the metal bipolar plate can effectively inhibit the further corrosion of the metal, the semiconductor properties of the metal oxide in the passivation film will lead to a decrease in surface conductivity. Apparently, all these factors are bound to cause some electric energy consumption and a reduction in the output power of the fuel cell stack, thereby affecting the durability of the battery pack. In order to meet the requirements of electrical conductivity and corrosion resistance at the same time, it is an effective method to prepare a modified layer on the surface of the metal bipolar plate, which will have an important impact on the development and application of polymer electrolyte membrane fuel cells. Obviously, the expensive noble metal modification layer is not suitable for the production of low-cost battery packs. Limited by the preparation process conditions, the nitride and oxide modified layers prepared by different methods such as PVD, CVD, electroless plating and electroplating often have unavoidable micropores and microcracks and other structural defects. These defects will undoubtedly cause localized corrosion of the metal bipolar plate and lead to peeling off of the modified layer, thereby significantly shortening the service life of the polymer electrolyte membrane fuel cell. Based on the fact that the existing surface modification methods are always more or less insufficient, there is no metal bipolar plate treated by surface modification that can meet the requirements of the current large-scale market application of polymer electrolyte membrane fuel cells. Therefore, the development of low-cost, high-surface conductivity and corrosion-resistant bipolar plates is still an inevitable path for polymer electrolyte membrane fuel cells, and it will inevitably have an important impact on its commercialization process.

Contents of the invention

The purpose of the invention is to provide a nano PPy (polypyrrole)-Au modified layer on the surface of a metal bipolar plate of a polymer electrolyte membrane fuel cell and a preparation method thereof. The method requires simple equipment, is easy to produce and process, and has low cost, and can meet the requirements of large-scale market applications.

The invention provides a method for preparing a nano PPy-Au modified fuel cell bipolar plate, which uses a metal material as a matrix and a nano PPy-Au modified layer on the surface. The modified layer is prepared by an electrochemical synthesis method, and has a dense surface without cracks and is closely combined with the matrix. The surface-modified metal bipolar plate can significantly improve the output power and service life of the polymer electrolyte membrane fuel cell.

In order to achieve the above object, the polymer electrolyte membrane fuel cell metal bipolar plate provided by the present invention is prepared by the following technical methods:

Using the electrochemical synthesis method, first put the metal substrate in the electrolyte solution to synthesize the modified layer, the temperature is 25°C, the current is 4mA/cm ² , the ultrasonic frequency is 24kHz, and the time is 10-30min; the above conditions can be better Oxidize pyrrole and reduce HAuCl ₄ ; before synthesizing the modified layer, the metal substrate should be pretreated according to the following steps: the metal substrate is sequentially polished with 400-2500 ^# sandpaper, and polished with diamond abrasive paste. In order to remove the grease and pollutants on the surface, ultrasonic cleaning is performed with acetone and alcohol solution for 15 minutes;

The electrochemical synthesis method adopts a three-electrode system: a metal platinum sheet is used as an auxiliary electrode, a saturated calomel electrode is used as a reference electrode, and a metal matrix is used as a working electrode;

The electrolyte solution is composed of 0.1mol/L oxalic acid, 0.1mol/L pyrrole monomer, 100ppm DBSA (dodecylsulfonic acid) and 3-10ppm HAuCl ₄ ; the electrolyte solution is prepared in the following order: first diethylene glycol Mix the acid and DBSA evenly, then add pyrrole purified by distillation, and finally add HAuCl ₄ .

In the above method provided by the present invention, the metal base material is stainless steel. Further, the stainless steel includes austenitic stainless steel, ferritic stainless steel and duplex stainless steel.

The polymer electrolyte membrane fuel cell metal bipolar prepared by the method provided by the invention is composed of a surface nanometer PPy-Au modified layer with a thickness of 2-5 μm and a metal matrix with a thickness of 0.1-3 mm. The surface nano PPy-Au composite modified metal bipolar plate prepared by the invention has a corrosion rate lower than 6μA/cm ² and a contact resistance lower than 10mΩ·cm ² .

The metal bipolar plate prepared by the method provided by the invention has the advantages that the preparation method of the metal bipolar plate modified by surface nanometer PPy-Au requires simple equipment, mature production technology, and is easy to realize mass production. The surface nano PPy-Au modified metal bipolar plate prepared by the present invention can meet its use requirements in terms of corrosion resistance and surface conductivity at the same time, and can be applied to the field of polymer electrolyte membrane fuel cells. The wide application of metal bipolar plates in electrolyte membrane fuel cells has important practical significance.

Detailed ways

Example 1

The nano PPy-Au modified polymer electrolyte membrane fuel cell metal bipolar plate provided in this example, deposits a nano PPy-Au modified layer on the AISI 304L stainless steel substrate according to the following steps:

1) Pretreatment: AISI 304L stainless steel substrate is polished with 400~2500 ^# sandpaper in sequence, and polished with diamond abrasive paste. In order to remove the grease and pollutants on the surface, ultrasonic cleaning is carried out with acetone and alcohol solution for 15 minutes.

2) Electrochemical synthesis adopts a three-electrode system: metal platinum sheet, saturated calomel electrode and metal matrix are used as auxiliary electrode, reference electrode and working electrode respectively;

Electrolyte solution preparation: first mix oxalic acid and DBSA evenly, then add distilled and purified pyrrole, and finally add HAuCl ₄ . In the electrolyte solution, the concentration of oxalic acid is 0.1M, the concentration of pyrrole is 0.1M, the concentration of DBSA is 100ppm, and the concentration of HAuCl ₄ is 7ppm.

3) Preparation of nano-PPy-Au modified layer: place the pretreated metal substrate in the above prepared electrolyte solution to synthesize the modified layer, the temperature is 25°C, the current is 4mA/cm ² , the ultrasonic frequency is 24kHz, and the time is 10min.

The nano-PPy-Au modified AISI 304L stainless steel bipolar plate prepared in this example has a modified layer thickness of 2 μm. The corrosion rate of the nano PPy-Au modified metal bipolar plate in the invention is lower than 4.5μA/cm ² , and the contact resistivity is lower than 3mΩ·cm ² .

Example 2:

The nano-PPy-Au modified polymer electrolyte membrane fuel cell metal bipolar plate provided in this example is prepared on the AISI 444 stainless steel substrate according to the following steps:

1) Pretreatment: AISI 444 stainless steel substrate is polished with 400~2500 ^# sandpaper in sequence, and polished with diamond abrasive paste. In order to remove the surface grease, ultrasonic cleaning was performed with acetone and alcohol solution for 15 minutes.

2) Electrochemical synthesis adopts a three-electrode system: metal platinum sheet, saturated calomel electrode and metal matrix are used as auxiliary electrode, reference electrode and working electrode respectively;

Electrolyte solution: Mix oxalic acid and DBSA evenly, then add distilled and purified pyrrole, and finally add HAuCl ₄ . In the electrolyte solution, the concentration of oxalic acid is 0.1M, the concentration of pyrrole is 0.1M, the concentration of DBSA is 100ppm, and the concentration of HAuCl ₄ is 5ppm.

3) Preparation of nano-PPy-Au modified layer: place the pretreated metal substrate in the above prepared electrolyte solution to synthesize the modified layer, the temperature is 25°C, the current is 4mA/cm ² , the ultrasonic frequency is 24kHz, and the time is for 20min.

The nano PPy-Au modified AISI 444 stainless steel bipolar plate prepared in this example has a modified layer thickness of 3.6 μm. The corrosion rate of the nano PPy-Au modified metal bipolar plate in the invention is lower than 4μA/cm ² , and the contact resistivity is lower than 5.3mΩ·cm ² .

Embodiment 3:

The nano PPy-Au modified polymer electrolyte membrane fuel cell metal bipolar plate provided in this example is prepared on the AISI 2205 stainless steel substrate according to the following steps:

1) Pretreatment: AISI 2205 stainless steel substrate is polished with 400~2500 ^# sandpaper in sequence, and polished with diamond abrasive paste. In order to remove the surface grease, ultrasonic cleaning was performed with acetone and alcohol solution for 15 minutes.

2) The commonly used three-electrode system was used for electrochemical synthesis: metal platinum sheet, saturated calomel electrode and metal substrate were used as auxiliary electrode, reference electrode and working electrode, respectively.

Electrolyte solution: Mix oxalic acid and DBSA evenly, then add distilled and purified pyrrole, and finally add HAuCl ₄ . In the electrolyte solution, the concentration of oxalic acid is 0.1M, the concentration of pyrrole is 0.1M, the concentration of DBSA is 100ppm, and the concentration of HAuCl ₄ is 10ppm.

3) Preparation of nano-PPy-Au modified layer: the pretreated metal substrate was placed in the above prepared electrolyte solution to synthesize the modified layer at a temperature of 25°C. In order to oxidize pyrrole monomer and reduce HAuCl ₄ , the current is 4mA/cm ² , the ultrasonic frequency is 24kHz, and the time is 25min.

The nano PPy-Au modified AISI 2205 stainless steel bipolar plate prepared in this example has a modified layer thickness of 4.4 μm. The corrosion rate of the nano PPy-Au modified metal bipolar plate in the invention is lower than 5μA/cm ² , and the contact resistivity is lower than 8.8mΩ·cm ² .

Claims (4)

1. The method for preparing the metal bipolar plate of the polymer electrolyte membrane fuel cell modified by nanometer PPy-Au is characterized in that it is prepared by electrochemical synthesis: the metal substrate is placed in the electrolyte solution to synthesize the modified layer, and the temperature is 25 ℃, the current is 4mA/cm ² , the ultrasonic frequency is 24kHz, and the time is 10-30min; The electrochemical synthesis method adopts a three-electrode system: a metal platinum sheet, a saturated calomel electrode and a metal matrix are respectively used as an auxiliary electrode, a reference electrode and a working electrode; The electrolyte solution is composed of 0.1M oxalic acid, 0.1M pyrrole, 100ppm DBSA and _3-10ppm HAuCl4; the electrolyte solution is prepared in the following order: first mix oxalic acid and DBSA evenly, then add pyrrole purified by distillation, and finally Add HAuCl ₄ ; Before the modified layer is synthesized, the metal substrate also undergoes the following pretreatment steps: the metal substrate is sequentially polished with 400-2500 ^# sandpaper, polished with diamond abrasive paste; and then ultrasonically cleaned with acetone and alcohol solution for 15 minutes. 2. The preparation method according to claim 1, characterized in that: the metal base material is austenitic stainless steel, ferritic stainless steel or duplex stainless steel. 3. The polymer electrolyte membrane fuel cell metal bipolar plate of the nanometer PPy-Au modification that method prepares as claim 1 or 2 is characterized in that: the surface of described metal substrate is nanometer PPy-Au modified layer; The corrosion rate of the metal bipolar plate of the polymer electrolyte membrane fuel cell modified by the nanometer PPy-Au is lower than 6 μA/cm ² , and the contact resistance is lower than 10 mΩ·cm ² . 4 . The nano-PPy-Au modified polymer electrolyte membrane fuel cell metal bipolar plate according to claim 3 , wherein the thickness of the nano-PPy-Au modified layer is 2-5 μm.